1. Field of the Invention
This invention relates to an impact pad for absorbing forces, and more particularly to an impact pad for absorbing forces having improved energy absorbent materials.
2. Description of the Prior Art
In the operation of docking a ship, because of the speed of approach, swells, currents and winds it is imperative to provide a protective docking system to reduce potential damage and impact to the ship, dock or pier. In the case of holding ships, such impact pads are used to protect both the holding ship and the smaller vessel transported therein.
Examples of fender protective structures for these types of applications can be found in commonly owned U.S. Pat. Nos. 4,923,550, 4,596,734, 4,679,517 all of which are issued to Kramer and are hereby fully incorporated herein by reference. The fender protective structures of these systems are comprised of a very hard outer plastic layer of ultra high molecular weight polyethylene (UHMWPE), a highly flexible, i.e. rubbery, intermediate elastomeric layer and a very hard base layer comprised of plastic. The base layer is necessary for installation purposes because a system with a conventional elastomeric layer bonded to a plastic layer is too flexible to work with, particularly when the elastomeric layer is partially counter bored.
Elastomer and plastic alloys are known in the marine art for utilization in the journal bearings that support the propeller shafts. More particularly, the alloy is used as stave material in the journal bearing. An example of such alloys is described in commonly owned U.S. Pat. No. 4,735,982 to Orndorff, Jr. Orndorff, Jr. teaches mixing a thermoset rubber compound and a thermoplastic, with the rubber compound having low friction as well as good oil and water resistant properties. Low friction is defined as material which develops hydrodynamic lubrication at normal shaft operating speeds. Use of low friction materials is important in bearing applications because shaft wear must be minimized. For this reason, higher friction rubber compounds are inappropriate in the alloy described in Orndorff, Jr.
Efforts to improve such fender protective systems have led to continuing developments to improve their versatility practicality and efficiency.
An object of the present invention is to provide two layer bonded fender protective structure.
Another object is to provide an improved bonded fender protective structure.
A general object is to provide an efficient and effective improved fender protective structure which is relatively hard, has a resilient layer with a delayed elastic response and is able to bulge upon impact for improved energy absorption.
According to the preferred embodiment of the present invention, a fender protective structure comprising an inner layer including a very hard top layer and a relatively hard elastomer and plastic alloy inner layer, the alloy being resilient and having a delayed elastic response. There provided voids in the alloy to reduce weight and to allow for expansion of the alloy upon impact. The fender protective structure thus includes an improved energy absorbing elastomer plastic alloy layer.
The present invention provides an improved fender protective structure having optimum resiliency for energy absorption and return and optimum rigidity for ease of installation.
The present invention further provides a two layer fender protective structure having a relatively hard, resilient with a delayed elastic response, structure which has room to expand on impact, and which slowly returns to its original shape for receiving subsequent impacts. The structure is instantaneously low in resilience, meaning it has high energy absorbing characteristics, and has a delayed elastic response or resilience, meaning it is able to regain its original dimensions in time delay after impact upon removal of an applied impact force, the delay being between 1 second to over an hour depending on circumstances.